1. Field of the Invention
The present invention relates to lift assemblies for raising and lowering a vehicle, and, more particularly, to a safety system for use with a multi-post lift assembly used to raise and lower a vehicle.
2. Description of the Related Art
Lift assemblies are well known in the art, particularly in the automotive servicing field, where a technician must often raise an automobile to a predetermined height above the ground in order to make appropriate repairs. Automotive lift assemblies can be constructed in a variety of configurations. For example, one type of lift assembly incorporates a centrally disposed hydraulic shaft that includes a plurality of arms. The arms are extendable to support the vehicle at prescribed load bearing positions. Single post systems, however, have a disadvantage of requiring an underground tunnel within which the hydraulic post can be fully retracted to allow the vehicle to be placed in position for lifting. Such an arrangement is complicated to construct and has an additional disadvantage of being permanently fixed the location constructed.
Other vehicle lift assemblies incorporate multiple posts that are positioned at predetermined locations for raising and lowering the vehicle. For example, one such lift arrangement incorporates two posts, one on either side of the vehicle. Each post includes arms that can be extended to support the vehicle at the load bearing positions. Another system incorporates four posts located at predetermined positions that define a rectangular area. A platform assembly is attached to the four posts and functions to support the vehicle during lifting and lowering operations. Lift assemblies that incorporate multiple posts typically include a lifting mechanism coupled to each post. The lifting mechanism can be mechanical, or hydraulic in nature. For example, a screw type or hydraulic piston arrangement can be provided to apply an appropriate force and allow the posts to raise and lower the vehicle in unison. Each post can be provided with a manual lock that prevents inadvertent movement of the vehicle, or the lift assembly, while the technician services the vehicle.
During normal operations, it is imperative that the lifting mechanism of each post operate in a synchronous manner. Any deviation in the operation of one post will result in the vehicle being tilted in an unsafe manner. This situation will often place the vehicle in an unsafe or unstable orientation wherein the vehicle can be damaged and/or the technician can be injured. In general, the greater the number of posts that are used in the vehicle lift assembly, the greater the probability that one of the lifting mechanisms will malfunction, hence causing the lift assembly to tilt to an unsafe orientation.
There are several conditions that can result in a lift assembly being tilted to an unsafe orientation. One of the most common conditions occurs when a technician inadvertently forgets to disengage the manual lock at one of the posts. If the lift platform is either raised or lowered, the post (or posts) that was left locked will be unable to move, while the remaining posts will be free to move in the selected direction. Hence, the lift platform will be tilted such that the vehicle will occupy a dangerous orientation. If the technician does not detect the malfunction, the lift platform will continue to tilt until the vehicle falls off or the maximum travel distance of the posts have been reached. Further, such a condition can result in damage to the lift assembly.
Accordingly, one disadvantage of current multi-post lift assemblies is the inability to detect when the lift platform has tilted to an unsafe orientation. Another disadvantage associated with current multi-post lift assemblies is the inability to automatically suspend operation of the lift mechanism when the lift platform has tilted to an unsafe orientation.